1. Field of the Invention
This invention relates to a combustion chamber for internal combustion engines, and more particularly to a combustion chamber for an internal combustion engine employing a spark plug for igniting a volatile fuel of low cetane number such as alcohol, gasoline or the like.
2. Description of the Prior Art
Generally, a Diesel engine spark assisting device as shown in FIG. 6 of the accompanying drawings (disclosed in Japanese Laid-Open Utility Model Application No. 58-178419) is known as a spark plug ignition means ensuring high thermal efficiency and good mileage.
According to this prior disclosure, in a combustion chamber b which is hollowed out of a piston top a, a spark plug f is located so as to have a spark position upstream of a sprayed zone d of a fuel injected toward the inner wall c of the combustion chamber b when viewed in the direction of a swirl S, and in the vicinity of the inner wall c.
With this arrangement, the time required to reach a spark position from an injection point by the sprayed fuel zone d which is carried away from the upstream side to the downstream side by the swirl S is utilized as a volatilization period for evaporating the fuel by contact with compressed air, thereby improving the degree of air-fuel mixing for attaining higher ignition and starting qualities.
However, the arrangement in this prior disclosure is not capable of igniting and burning a volatile fuel of low cetane number such as alcohol, gasoline or the like. A volatile fuel is instantly volatilized and dispersed upon being injected into the combustion chamber due to its high volatility, so that it is necessary to increase the amount of fuel injection or to adjust the air-fuel ratio by throttling intake air to enrich the air-fuel mixture into a concentration suitable for sparking ignition and flame propagation.
The throttling of intake air, however, increases the pumping job of the internal combustion engine, and is therefore undesirable from the standpoint of mileage and output qualities. Because of these disadvantages, there has been a demand for new techniques which can distribute an air-fuel mixture of a suitable concentration in terms of ignition and combustion qualities to the neighborhood of the sparking terminal of a spark plug.